1. Field of the Invention
This invention relates to a method and an apparatus for classifying music pieces represented by data stored in, for example, a recording medium, a server, or a storage unit. This invention also relates to a computer program for classifying music pieces.
2. Description of the Related Art
Japanese patent application publication number 2002-278547 discloses a system composed of a music-piece registering section, a music-piece database, and a music-piece retrieving section. The music-piece registering section registers audio signals representing respective music pieces and ancillary information pieces relating to the respective music pieces in the music-piece database. Each audio signal representing a music piece and an ancillary information piece relating thereto are in a combination within the music-piece database. Each ancillary information piece has an ID, a bibliographic information piece, acoustic feature values (acoustic feature quantities), and impression values about a corresponding music piece. The bibliographic information piece represents the title of the music piece and the name of a singer or a singer group vocalizing in the music piece.
The music-piece registering section in the system of Japanese application 2002-278547 analyzes each audio signal to detect the values (the quantities) of acoustic features of the audio signal. The detected acoustic feature values are registered in the music-piece database. The music-piece registering section converts the detected acoustic feature values into values of a subjective impression about a music piece represented by the audio signal. The impression values are registered in the music-piece database.
The music-piece retrieving section in the system of Japanese application 2002-278547 responds to user's request for retrieving a desired music piece. The music-piece retrieving section computes impression values of the desired music piece from subjective-impression-related portions of the user's request. Bibliographic-information-related portions are extracted from the user's request. The computed impression values and the extracted bibliographic-information-related portions of the user's request are combined to form a retrieval key. The music-piece retrieving section searches the music-piece database in response to the retrieval key for ancillary information pieces similar to the retrieval key. Music pieces corresponding to the found ancillary information pieces (the search-result ancillary information pieces) are candidate ones. The music-piece retrieving section selects one from the candidate music pieces according to user's selection or a predetermined selection rule. The search for ancillary information pieces similar to the retrieval key has the following steps. Matching is implemented between the extracted bibliographic-information-related portions of the user's request and the bibliographic information pieces in the music-piece database. Similarity between the computed impression values and the impression values in the music-piece database are calculated. From the ancillary information pieces in the music-piece database, ones are selected on the basis of the matching result and the calculated similarities.
In the system of Japanese application 2002-278547, the registered impression values tend to be out of harmony with human sensations since they are derived from the acoustic features of the audio signals. The system of Japanese application 2002-278547 tend to be inoperative for audio signals representative of readings of poems and stories.
Japanese patent application publication number 2004-326840 discloses a music data selection system including a data analyzer. For every music data block representing one music piece, the data analyzer subjects lyrics in the music data block to a morphological analysis to convert them into feature quantities concerning impression words. Specifically, the data analyzer extracts impression words from the lyrics in the music data block. According to a thesaurus dictionary, the data analyzer separates the extracted impression words into thesaurus groups of synonyms. For each thesaurus group, the data analyzer computes a frequency at which related synonyms appear. The computed appearance frequency is a feature quantity. Thus, for every music data block representing one music piece, the data analyzer obtains impression words and appearance frequencies (feature quantities) of the obtained impression words.
The system of Japanese application 2004-326840 includes a data deciding portion which responds to a keyword set by a user. For selected ones among music data blocks representing respective music pieces, the data deciding portion calculates the value of a correlation between the keyword and each of impression words obtained by the data analyzer. For each of the selected music data blocks, the data deciding portion computes a score from the calculated values of correlations between the keyword and the impression words, and the appearance frequencies of the impression words. The data deciding portion makes a play list in which the selected music data blocks are arranged in the order of computed score.
The system of Japanese application 2004-326840 is ineffective for music data blocks representing music pieces without words.
Japanese patent application publication number 6-290574/1994 discloses a music-piece retrieval apparatus in which a primary index of each music piece is a bibliographic item about the music piece such as a title thereof. Acoustic features such as a rhythm-related feature and a chord-related feature are derived from audio data representing each music piece. The derived acoustic features are labeled a secondary index of the music piece. A tertiary index of each music piece is generated on the basis of the secondary index thereof. The tertiary index represents subjective and emotional features of the music piece. There are storages which store primary, secondary, and tertiary indexes of many music pieces. To implement retrieval, a user inputs conditions of a desired music piece which are designed to correspond to primary, secondary, and tertiary indexes of the desired music piece. The inputted conditions are compared with the stored primary, secondary, and tertiary indexes of the music pieces. The comparison is to find, among the stored primary, secondary, and tertiary indexes of the music pieces, a set of primary, secondary, and tertiary indexes of at least one music piece which matches the inputted conditions. The music piece corresponding to the found set of primary, secondary, and tertiary indexes is selected as a retrieval result regarding the desired music piece.
In the music-piece retrieval apparatus of Japanese application 6-290574/1994, the derivatives of the acoustic powers of audio data representing each music piece are computed for each prescribed time interval (each frame). The autocorrelation of the power derivatives is calculated. The calculated autocorrelation varies as a function of a frequency parameter or a period parameter. A value of the frequency parameter or the period parameter is decided at which the calculated autocorrelation is maximized. One of the derived acoustic features is generated on the basis of the decided value of the frequency parameter or the period parameter.